The proposed research utilizes in vitro and in vivo assays to identify downstream signaling mechanisms of a specific receptor-ligand (EphB1-ephrin-B2) interaction that patterns binocular vision by mediating repulsion of ventrotemporal (uncrossed) retinal axons at the optic chiasm. To demonstrate the specificity and sufficiency of this interaction, EphB1 and EphB2 will be introduced into EphB1 null retinal explants in vitro and embryonic retinae in vivo, and axon projections and responses to ephrin-B2 substrates will be characterized. EphB1 can activate numerous downstream signaling pathways in heterologous systems, but it is unknown which of these are biologically relevant. A series of experiments will characterize the role of growth cone calcium transients in mediating EphB1 repulsion from ephrin-B2. In tandem, additional studies will use pharmacological methods to identify which pathways are required for EphB1-mediated repulsion from ephrin-B2. Lastly, a series of mutations in the EphB1 receptor will be introduced in these same assays to reveal which domains are responsible for transducing EphB1 activation into repulsion. These experiments will increase our knowledge in the fields of axon guidance and growth cone dynamics. [unreadable] [unreadable]